<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>demo-2</title>
</head>

<body>
  <script>
    let money = 100
    while (true) {
      let re = +prompt(`
            请您选择操作：
            1.存钱
            2.取钱
            3.查看余额
            4.退出`)
      if(re === 4){
          break
        }
      switch (re) {
        case 1:
          let cun = +prompt('请您输入存款金额')
          money = money + cun
          break
        case 2:
          let qu = +prompt('请您输入取款金额')
          money = money - qu
          break
        case 3:
          alert(`余额为：${money}`)
          break
      }
    }



  </script>  
</body>
</html>